How to set up Thunderbird

The instructions and screenshots in this setup guide are for the latest version of Thunderbird, which you can download for free for Windows, macOS, or Linux.

You can easily add your Fastmail account to Thunderbird using the setup guide in the Settings → Migration → Apps & Setup guides screen. The general setup instructions are below.

Thunderbird needs its own app password to access your information. If you use your normal password in Thunderbird, syncing won't work and you will see a password error.

Set up your email

1. Open Thunderbird. The Set Up an Existing Email Account dialog box will appear. If it doesn't, select Local Folders in the sidebar on the left, then under the Choose What to Set Up heading in the page that appears, click the Email link.

2. Fill in your name, email address, and app password:

   • Your name: Whatever name you want others to see on the email you send.
   • Email address: Your full Fastmail username, including the domain.
   • Password: Your Thunderbird app password. (What is an app password?)

   Click Continue. Thunderbird will find the server settings.

3. Click Done.

4. Thunderbird will then fetch the list of your folders and start synchronizing your mail. If you wish to sync calendars, this can be done now (see below for further instructions).

Thunderbird 115 and OAuth2

If you are using Thunderbird 115, there are some additional steps due to added support for OAuth2.

To start, please make sure cookies are enabled in Thunderbird. Cookies must be enabled for OAuth2 to work. You can enable cookies in Thunderbird by going to Settings > Privacy & Security > Web Content > Accept cookies from sites.

If you do not want to set up Thunderbird to accept cookies from all sites, then you can specifically make an exception for Fastmail. You can do so by going to Settings > Privacy & Security > Web Content and clicking Exceptions..., then adding app.fastmail.com and api.fastmail.com as exceptions.

After following the above setup steps and clicking Done in Step 3, you will see a pop-up window where you'll be prompted to enter your Fastmail login credentials. Here, you'll need to enter your username and your account's master password (not the app password you generated), then click Log in.

If you have 2FA enabled for your account, you'll be prompted to authenticate using your two-step verification method. On the following screen, you'll be asked if you want to grant Thunderbird permission to access your Fastmail account. Click Allow. After this, Thunderbird will fetch your folders and synchronize your mail as described in Step 4 above.

Adding your other email addresses

To use a different email address that is not your Fastmail username:

1. Open Thunderbird. Click your account name in the sidebar (just above the Inbox).
2. Click View settings for this account.
3. Click Manage Identities…, then click Add…
4. Fill in Your Name and Email Address with the name and email you want your messages to come from.
5. Click OK to save the new identity. If you want it to be the default, click Set Default then close the identities panel. Click OK to close the account settings dialog.

You will now be able to choose the address you added to send messages from when you compose new messages in Thunderbird.

Set up your calendar and contacts

You can sync Fastmail calendars and contacts during initial setup of your account in Thunderbird.

1. When you have set up your mail account and reach the Account successfully created screen, Thunderbird will then search for any other services you can link to for your account. If Thunderbird detects that your account has any address books or calendars that can be linked, you should see these options show up under Connect your linked services.
   • If you wish to set up contacts, click on the Address Book dropdown. You can choose which address books to link by clicking the Connect button next to the corresponding address books.

   • If you wish to set up calendars, click on the Calendars dropdown. You can choose which calendars to link by clicking the Connect button next to the corresponding calendar. A popup window will appear showing settings you can choose for linking this calendar. Choose your preferred settings and click Connect to complete the link.

2. After you've linked the preferred services, click Finish.

If Thunderbird does not automatically detect your Fastmail account's calendars or contacts, you'll need to manually add them using CalDAV and CardDAV. 

To add a calendar manually, please follow the below steps:

1. Select New calendar on Thunderbird's calendar screen.
2. Select On the network, then press Continue.
3. Enter your full Fastmail username and enter the URL https://caldav.fastmail.com/ as the location, then click Find Calendars. 
4. Enter your Thunderbird app password and click Ok.
5. Select the calendars you'd like to add and then click Subscribe.

To add your contacts manually, go to the Address Book screen in Thunderbird and follow the directions below. 

1. Click the dropdown arrow next to New Address Book.
2. Select Add CardDAV Address Book from the dropdown list.
3. Enter your full Fastmail username and enter the URL https://carddav.fastmail.com/ as the location, then click Continue.
4. Select whether you want to import your Personal address book, Global address book, or both and then click Continue.

Display all folders

When you set up your account on Thunderbird, the default display for folders is to show only subscribed folders. To have Thunderbird display all of your folders, you'll need to make a change in your Account Settings.

1. Open Thunderbird and go to Account Settings.
2. Select your Fastmail account from the list, then click Server Settings under it.
3. In the Server Settings section, click Advanced...
4. You'll see Show only subscribed folders enabled. Disable that by unchecking the checkbox.